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EC number: 200-867-7
CAS number: 75-38-7
VDF undergoes reactions with hydroxyl radicals in the atmosphere, the calculated rate constant with is 2.27E-12 cm3/molecule.sec.
In the atmosphere, VDF
is considered to be degraded mainly by reaction with OH-radicals in the
troposphere. Atmospheric degradation rate constants ranged from 2.0 to
2.5E-12 cm3/mol. s. The calculated rate constant with AOPWIN™v1.92a
(U.S. EPA, 2008) is 2.27E-12 cm3/molecule. ses, the half life of VDF,
based on a 12-hr day with an OH radical concentration of 1.5E6 OH/cm3,
is 4.7 days (see Annexes 2 and 3 for the QMRF and QPRF).
The degradation of VDF
in the lower atmosphere will be initiated mainly by reaction with
naturally occurring hydroxyl radicals. The rate constant (kOH) for this
process was determined by Howard (1976) at low pressures, in the
"fall-off" region (0.001 - 0.01 atm). Extrapolating Howard’s values to
atmospheric pressure gives kOH = 2.4E–12 cm3/molecule.sec at 296 K.
Krejci (1995) found a similar value, kOH = 2.5E–12 cm3/molecule.sec, at
the same temperature.Baasandorj
et al. (2010) measured
a rate constant at room temperature (296 K) of 2.79 E-12
Assuming a mean
tropospheric OH concentration of 1E06 molecules/cm3, the half-life of
VDF is calculated to be approximately 3.3 days. However, this is a
global annual average value and, for such a short-lived species as VDF,
the actual atmospheric persistence will vary greatly (with latitude and
season of year, even time of day), mainly on account of variations in
the local OH concentration.
Becker et al (1974)
determined the rate constant for reaction of VDF with ozone to be 8E–20
cm3/molecules at ambient temperature. Assuming the mean tropospheric O3
concentration to be 7.5E11 molecules/cm3, the half-life of VDF with
respect to reaction with O3 is 134 days. This reaction will therefore
make a negligible contribution to the atmospheric degradation of VDF.
absorption of VDF falls off abruptly above 190 nm (Bélanger and
Sandorfy, 1971; Sirkin and Pimentel, 1984) so that photolysis at
wavelengths reaching the troposphere (> 290 nm) is not significant.
(COF2) and formaldehyde (HCHO) are predicted to be degradation products,
irrespective of the regioselectivity of the addition of OH radicals to
VDF (ECETOC, 2005). Formaldehyde occurs naturally in the atmosphere and
its fate is not discussed further. Carbonyl fluoride will not be
photolysed or undergo chemical reaction in the gas phase of the
atmosphere, but will be removed by uptake into cloud droplets and
subsequent hydrolysis to CO2 and HF, within a few weeks (Cox et al,
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